1. Field of the Invention
This invention concerns a device which can skim a relatively thin top surface layer of liquid which lies atop a bottom layer of liquid, in for example, a body of water. The invention more particularly concerns a skimming device that is self-leveling and can be used onboard a boat so as to skim a top liquid layer from atop a bottom liquid layer in a large, open body of the bottom liquid layer.
2. Discussion of the Background
Related skimmers have a number of shortcomings which can result in recovery of a top liquid layer and a bottom liquid layer, such as oil and water, respectively, which contains a large amount of the bottom liquid layer (water) when it is to be desired to skim only the top liquid layer (oil). Also, related skimming devices are known to be dynamically unstable. Ideally, a skimming device provides for skimming the lowest possible amount of skimmed bottom liquid layer (water) and/or entrains the lowest possible amount of air while skimming the maximum amount of the top liquid layer (oil).
In one type of related device, skimmers were used to remove, for example, a floating layer of oil resting atop a body of water due to an oil spill. In this device, the system would literally suck or vacuum the top liquid layer of oil from the body of water. The vacuum device, ideally, would be located as near as possible to the surface of the oil layer to maximize the ratio of oil to water removed, yet it would be located far enough away from the surface of the oil so that it would not be likely that water would be vacuumed. This is desirable since a large ratio of oil to water reduces the time and effort spent on any subsequent oil/water separation operations. However, locating the vacuuming device far enough away from the surface of the top liquid layer, so as to minimize the amount of water vacuumed, increases the possibility of entraining air into the system due to water level fluctuations. Entrained air introduced into the pumping system can cause pump cavitation, air lock, and interruption of operation. Thus, the location of the vacuuming device relative to the surface of the top liquid layer is a compromise between minimizing the volume of air entrained or minimizing the volume of water removed.
In another type of related device a hollow, general-shaped vessel is rotatably attached to a floating platform which is used in a small reservoir. The general-shaped vessel has an open section, the lower most edge forming a weir. The general-shaped vessel, when viewed from one side end thereof, tilts clockwise when the vessel is not filled with liquid, at such a time liquid flows over the weir and is introduced into the interior of the general-shaped vessel. When the gravitational moment or torque of the liquid about the pivot point exceeds the buoyancy moment which acts in the opposite, counterclockwise, direction the general-shaped vessel rotates counterclockwise so as to stop the influx of fluid into the general-shaped vessel. A suction line leading into the general-shaped vessel is used to evacuate any liquid contained inside the general-shaped vessel. When the vessel begins to empty the general-shaped vessel rotates clockwise, thus introducing more liquid into the interior of the general-shaped vessel once the buoyancy force moment, which acts in a clockwise direction, exceeds the gravitational moment of the liquid remaining inside the general-shaped vessel. In practice, it has been found, as disclosed by the related art, that when the input supply of liquid to the reservoir fluctuates fairly rapidly the skimmer may rather abruptly rock up and down continuously, and hard stops are employed to limit the magnitude of the rotation of the general-shaped vessel.
Thus, there is a need for a skimmer which does not entrain air, does not skim too much water along with the desirably skimmed oil, and acts dynamically stable when faced with a fluctuating input supply of liquid.